mysql_pconnect() drops the open connection into a pool that can be used by any other request to the same process. As such, each worker keeps the connection open until it dies. This can be acceptable if you keep the number of workers low, but as soon as you raise the number of workers then you're better off switching to mysql_connect(). It will take slightly longer per request since the connection has to be made each time, but you will only create as many connections as there are requests, not workers.